1. Field of the Invention
This invention relates to a mobile phone antenna, and more particularly to a multi-band mobile phone antenna assembly, which can increase effectively the bandwidth of the antenna.
2. Description of the Related Art
Recent mobile phones tend to have a compact size and an attractive appearance. Therefore, built-in type antennas, which are concealed within mobile phones, have developed rapidly. For example, referring to FIG. 1, a conventional planar inverted F-shaped antenna (PIFA) 1 is shown to include a metal strip, which is formed with a slot 10 that has an open end 101 and a closed end 102 and which includes a first antenna portion 11, a second antenna portion 12, a signal feeding point 13 disposed between the first and second antenna portions 11, 12, and a grounding point 14 disposed adjacent to the signal feeding point 13. The first antenna portion 11 is a low frequency antenna, and is applicable in a GSM 900 system. The second antenna portion 12 is a high frequency antenna, and is applicable in a DCS1800 system. The signal feeding point 13 and the grounding point 14 are in electrical connection with a circuit board (not shown) in a mobile phone. The bandwidth and gain of the antenna 1 are proportional to the size of the antenna 1 and the distance between the antenna 1 and the ground. The size of the conventional PIFA is too small to have a wide bandwidth.
To overcome this problem, referring to FIG. 2, a parasitic element 2 can be coupled parasitically to the second antenna portion 12 so as to increase the resonant frequency of the latter. As such, the second antenna portion 12 is applicable in both DCS1800 and PCS1900 systems. However, the bandwidth of the conventional PIFA 1 is widened only within the high frequency band of the second antenna portion 12 but not within the low frequency band of the first antenna portion 11.
The object of this invention is to provide a built-in multi-band mobile phone antenna, which can reduce influence on antenna gain due to distance between the antenna and the ground, and which can increase the bandwidths of both high and low frequency bands.
According to this invention, a built-in multi-band mobile phone antenna assembly includes a patch antenna, a loop antenna disposed adjacent to the patch antenna, and a parasitic element disposed adjacent to both the patch antenna and the loop antenna and coupled parasitically to the patch antenna. As such, the influence of the distance between the antenna and the ground is reduced with respect to the antenna gain, and the bandwidth of the antenna is widened.
The patch antenna serves as a low frequency antenna. The loop antenna serves as a high frequency antenna. The bandwidths of the patch and loop antennas are widened.